Determining impedance-related phenomena in vibrating actuator and identifying device system characteristics based thereon

ABSTRACT

A method, including determining a change in an actuator impedance based on a change in an electrical property of a system of which the actuator is apart, and determining one or more system characteristics based on the change in the actuator impedance.

CROSS-REFERNCE TO RELATED APPLICATIONS

This application is a Divisional application of U.S. patent applicationSer. No. 15/874,802, filed Jan. 18, 2018, which is a Continuationapplication of U.S. patent application Ser. No. 14/212,116, filed Mar.14, 2014 (now U.S. Pat. No. 9,900,709), naming Martin E. Hillbratt as aninventor, which claims priority to U.S. Provisional Application No.61/788,638, filed Mar. 15, 2013. The entire contents of each applicationare incorporated herein by reference in their entirety.

BACKGROUND Field of the Technology

The present technology relates generally to hearing prostheses, and moreparticularly, to identifying system characteristics such as vibratingactuator characteristics, implant characteristics, couplingcharacteristics or other system characteristics in a hearing prosthesis.

Related Art

Hearing loss, which may be due to many different causes, is generally oftwo types, conductive and sensorineural. Sensorineural hearing lossoccurs when there is damage to the inner ear, or to the nerve pathwaysconnecting the inner ear to the brain. Conductive hearing loss occurswhen the normal mechanical pathways that provide sound to the cochleaare impeded, for example, by damage to the ossicular chain or ear canal.However, individuals suffering from conductive hearing loss may retainsome form of residual hearing because the hair cells in the cochlea mayremain undamaged. As a result, individuals suffering from conductivehearing loss typically receive a hearing prosthesis that generatesmechanical motion of the cochlea fluid. Still other individuals sufferfrom mixed hearing losses, that is, conductive hearing loss inconjunction with sensorineural hearing. Such individuals may have damageto the outer or middle ear, as well as to the inner ear (cochlea).Individuals suffering from conductive hearing loss typically receive anacoustic hearing aid. Unfortunately, not all individuals suffer fromconductive hearing loss are able to derive suitable benefit from hearingaids.

Another type of hearing prosthesis delivers mechanical stimulation to arecipient. Such mechanical stimulating hearing prostheses include middleear implants that deliver mechanical vibrations to the ossicles of themiddle ear or directly to the cochlea, semicircular canals, vestibule orother part of the inner ear. Another type of mechanical stimulatinghearing prosthesis, commonly referred to as a bone conduction devices,converts a received sound into mechanical vibrations that are deliveredto the cranium, mandible or other part of the skull. The vibrations aretransferred through the bones of the skull to the cochlea resulting in ahearing percept.

SUMMARY

According to an exemplary embodiment, there is a method, comprisingdetermining a change in an actuator impedance based on a change in anelectrical property of a system of which the actuator is apart, anddetermining one or more system characteristics based on the change inthe actuator impedance.

According to another exemplary embodiment, there is a method comprisingapplying a first stimuli to an actuator that is part of a system,determining a change in voltage across a shunt component in series withthe actuator, determining one or more system characteristics based onthe change in voltage.

According to another exemplary embodiment, there is a hearingprosthesis, the prosthesis comprising an actuator, a signal generatorconfigured to provide a signal to the actuator to cause actuation of theactuator, and a control circuit configured to direct the signalgenerator to apply a first stimuli to the actuator, wherein the controlcircuit is configured to determine a change in an electrical property ofa system of which the actuator is apart, and determine animpedance-related phenomenon of the actuator based on the determinedchange in the electrical property.

According to another exemplary embodiment, there is a method fordetermining a state of an actuator of a hearing prosthesis configured todeliver mechanical stimulation to a recipient, comprising, measuring afirst voltage across a shunt component in series with the actuator,comparing the first voltage with a second voltage, and determining oneor more characteristics of the hearing prosthesis.

BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments of the present technology are described below with referenceto the attached drawings, in which:

FIG. 1A is a perspective view of a percutaneous bone conduction hearingprosthesis in which embodiments of the present technology may beimplemented;

FIG. 1B is a perspective view of a middle ear hearing prosthesis inwhich embodiments of the present technology may be implemented;

FIG. 2A illustrates a simplified block diagram of a housing of anexemplary bone conduction device in which embodiments of the presenttechnology may be implemented;

FIG. 2B illustrates a simplified block diagram of a stimulator unit andstimulation arrangement of a middle ear implant in which embodiments ofthe present technology may be implemented;

FIG. 3A illustrates a flow chart of an exemplary method for determininga change in impedance across an actuator using a shunt component;

FIG. 3B is a flow chart of another exemplary method for determining achange in impedance across an actuator using a shunt component;

FIG. 3C is a flow chart of another exemplary method for determining achange in impedance across an actuator using a shunt component;

FIG. 4 illustrates a partial circuit diagram representative of theactuator and shunt resistor relationship in accordance with embodimentsof the present technology;

FIG. 5A is frequency responses for the magnitude of the impedance of anactuator in which embodiments of the present technology may beimplemented; and

FIG. 5B is frequency responses for the phase of the impedance of anactuator in which embodiments of the present technology may beimplemented.

DETAILED DESCRIPTION

Aspects and embodiments of the present technology are directed tomechanical stimulating hearing prostheses, and more particularly, todetermining characteristics, behavior or state of an actuator of theprosthesis based on changes in the mechanical impedance of the actuator.

The mechanical impedance of an actuator in a mechanical stimulatinghearing prosthesis may be used to improve the accuracy of mechanicalstimulation delivered to the recipient and may be used to detect acharacteristic, behavior or state of the system (e.g. the type ofsystem, if an implanted actuator, turned off or disconnected, thestability of the system, etc.). More specifically, a change in impedanceof the actuator may indicate a change in such a characteristic, behavioror state (as referred to herein, the term “characteristic” may alsorefer to the “status,” “state,” or “behavior” of the actuator, or viceversa). For example, an increase in impedance of the actuator mayindicate that an implanted actuator has become more unstable or, for amore drastic increase, that the implanted actuator has been detachedfrom the recipient.

Exemplary embodiments are disclosed for measuring impedance and changesin impedance of an actuator in such a hearing prosthesis. A shuntcomponent, such as a shunt resistor, may be connected in series to theactuator, and the voltage measured across the shunt resistor in responseto a stimulus may be used to determine the impedance across theactuator. Exemplary embodiments of the present technology are describedherein with respect to two exemplary mechanical stimulating hearingprostheses, namely an exemplary bone conduction device illustrated inFIG. 1A, and an exemplary middle ear hearing prosthesis illustrated inFIG. 1B.

FIG. 1A is a perspective view of a percutaneous bone conduction device100A in which embodiments of the present technology may beadvantageously implemented. As shown, the recipient has an outer ear101, a middle ear 102 and an inner ear 103. Elements of outer ear 101,middle ear 102 and inner ear 103 are described below, followed by adescription of bone conduction device 100A.

In a fully functional human hearing, outer ear 101 comprises an auricle109 and an ear canal 106. A sound wave 107 is collected by auricle 109and channeled into and through ear canal 106. Disposed across the distalend of ear canal 106 is a tympanic membrane 104 which vibrates inresponse to sound wave 107. This vibration is coupled to oval window orfenestra ovalis 110 through three bones of middle ear 102, collectivelyreferred to as the ossicles 111 and comprising the malleus 112, theincus 113 and the stapes 114. Bones 112, 113 and 114 of middle ear 102serve to filter and amplify sound wave 107, causing oval window 110 toarticulate, or vibrate. Such vibration activates tiny hair cells (notshown) that line the inside of cochlea 115. Activation of the hair cellscauses appropriate nerve impulses to be transferred through the spiralganglion cells and auditory nerve 116 to the brain (not shown), wherethey are perceived as sound.

FIG. 1A also illustrates the positioning of bone conduction device 100Arelative to outer ear 101, middle ear 102 and inner ear 103 of arecipient of device 100A. As shown, bone conduction device 100A includesexternal component 145 which may be positioned behind outer ear 101 ofthe recipient and comprises a sound input device 126 to receive soundsignals. Sound input device may comprise, for example, a microphone,telecoil, etc. Sound input device 126 may also be a component thatreceives an electronic signal indicative of sound, such as, for example,from an external audio device. For example, sound input device 126 mayreceive a sound signal in the form of an electrical signal from an MP3player electronically connected to sound input device 126. Sound inputdevice may be located, for example, on the device, in the device, or ona cable extending from the device.

Bone conduction device 100A may comprise a sound processor, a vibratingactuator and/or various other operational components which facilitateoperation of the device. More particularly, bone conduction device 100Aoperates by converting the sound received by sound input device 126 intoelectrical signals. These electrical signals are utilized by the soundprocessor to generate control signals or driver signals (also referredto herein as “stimuli”) that cause the actuator (located in housing 124)to vibrate. These control signals are provided to the vibratingactuator. As described below, the vibrating actuator converts thesignals into mechanical vibrations used to output a force for deliveryto the recipient's skull.

Bone conduction device 100A further includes a housing 124, a coupling161 and an implanted anchor 162 configured to attach the device to therecipient. In the specific embodiments of FIG. 1A, coupling 161 isattached to implanted anchor 162, which is implanted in the recipient.In the illustrative arrangement of FIG. 1A, implanted anchor 162 isfixed to the recipient's skull bone 136. Coupling 161 extends fromimplanted anchor 162 and bone 136 through muscle 134, fat 128 and skin132 so that housing 124, or a component within housing 124, may beattached thereto. Implanted anchor 162 facilitates efficienttransmission of mechanical force to the recipient. It would beappreciated that embodiments of the present technology may beimplemented with other types of couplings and anchor systems, as well asother types of bone conduction devices, such as, for example, an activeor passive transcutaneous bone conduction device (including, forexample, transmission of data to the recipient's skull using a magneticfield, a magnet attached to the outside of the recipient's head and ananother magnet implanted in the recipient's skull).

Embodiments of the present technology may also be implemented to includea middle ear hearing prosthesis, as noted. A middle ear hearingprosthesis generates vibrations that are directly coupled to the middleear of a recipient and thus bypasses the outer ear of the recipient.FIG. 1B is a perspective view of an exemplary middle ear hearingprosthesis 100B in accordance with embodiments of the presenttechnology.

Middle ear hearing prosthesis 100B comprises an external component 142that is directly or indirectly attached to the body of the recipient,and an internal component 144 that is temporarily or permanentlyimplanted in the recipient. External component 142 typically comprisesone or more sound input devices, such as microphones 224 for detectingsound, a sound processing unit 146, a power source (not shown), and anexternal transmitter unit (also not shown). The external transmitterunit is disposed on the exterior surface of sound processing unit 146and comprises an external coil (not shown). Sound processing unit 146processes the output of microphones 224 and generates encoded signals,sometimes referred to herein as encoded data signals, which are providedto the external transmitter unit. For ease of illustration, soundprocessing unit 146 is shown detached from the recipient.

Internal component 144 comprises an internal receiver unit 148, astimulator unit 149, and a stimulation arrangement 150B. Internalreceiver unit 148 and stimulator unit 149 are hermetically sealed withina biocompatible housing, sometimes collectively referred to herein as astimulator/receiver unit.

Internal receiver unit 148 comprises an internal coil (not shown), andpreferably, a magnet (also not shown) fixed relative to the internalcoil. The external coil transmits electrical signals (i.e., power andstimulation data) to the internal coil via a radio frequency (RF) link.The internal coil is typically a wire antenna coil comprised of multipleturns of electrically insulated single-strand or multi-strand platinumor gold wire. The electrical insulation of the internal coil is providedby a flexible silicone molding (not shown). In use, implantable receiverunit 132 is positioned in a recess of the temporal bone adjacent auricle109 of the recipient in the illustrated embodiment.

In the illustrative prosthesis, stimulation arrangement 150B isimplanted in middle ear 102. For ease of illustration, ossicles 111 havebeen omitted from FIG. 1B. However, it should be appreciated thatstimulation arrangement 150B is implanted without disturbing ossicles111 in the illustrated embodiment.

Stimulation arrangement 150B comprises an actuator 140, a stapesprosthesis 152 and a coupling element 151. In this embodiment,stimulation arrangement 150B is implanted and/or configured such that aportion of stapes prosthesis 152 abuts an opening in one of thesemicircular canals 125. For example, in the illustrative prosthesis,stapes prosthesis 152 abuts an opening in horizontal semicircular canal123. It would be appreciated that in other middle ear hearingprostheses, stimulation arrangement 150B may be implanted such thatstapes prosthesis 152 abuts an opening in posterior semicircular canal127 or superior semicircular canal 129. It would also be appreciatedthat stimulation arrangement 150B may be implanted such that stapesprosthesis 152 abuts round window 121 or other structure that willresult in the delivery of mechanical energy to the hydro-mechanicalsystem of the cochlea.

As noted above, a sound signal is received by one or more microphones224, processed by sound processing unit 146, and transmitted as encodeddata signals to internal receiver 148. Based on these received signals,stimulator unit 149 generates drive signals which cause actuation ofactuator 140. This actuation is transferred to stapes prosthesis 152such that a wave of fluid motion is generated in horizontal semicircularcanal 123. Because, vestibule 120 provides fluid communication betweenthe semicircular canals 125 and the median canal, the wave of fluidmotion continues into median canal, thereby activating the hair cells ofthe organ of corti. Activation of the hair cells causes appropriatenerve impulses to be generated and transferred through the spiralganglion cells (not shown) and auditory nerve 116 to the brain (also notshown) where they are perceived as sound.

As noted, the prostheses of FIGS. 1A and 1B are but two exemplarymechanical stimulating hearing prostheses. Embodiments of the presenttechnology may be implemented in connection with other types ofmechanical stimulating hearing prostheses now or later developed.However, for ease of description, the following description ofembodiments of the present invention are described, where applicable,with reference to a percutaneous bone conduction device an example ofwhich, bone conduction device 100A, is introduced above with referenceto FIG. 1A.

As noted, the impedance of an actuator in a vibrating hearingprosthesis, such as those described in FIG. 1A, may be used to improvethe accuracy of mechanical stimulation delivered to the recipient andmay be used to detect a characteristic, behavior or state of the system(e.g. the type of system, if an implanted actuator, turned off ordisconnected, the stability of the system, etc.). More specifically, achange in mechanical impedance of the actuator may represent a change ina state or characteristic of the actuator or the hearing prosthesis as awhole. Furthermore, a change in electrical impedance presented by theactuator indicates a corresponding change in mechanical impedance of theactuator. As is known to one of skill in the art, resonance refers tothe tendency of a system to oscillate with larger amplitude at somefrequencies than at others. Therefore, the frequency response of theelectrical impedance of an actuator is used to observe such changes inmechanical impedance between different frequencies, different times anddifferent actuators. Exemplary frequency responses are discussed withrespect to FIGS. 5A and 5B.

FIG. 5A illustrates a frequency response for the magnitude of theelectrical impedance (hereinafter “impedance magnitude”) of, forexample, the actuator in FIG. 1A. FIG. 5B illustrates the correspondingfrequency response for the phase of the impedance of the actuators, andwill be described further below. Frequency responses 505, 510 and 515may be obtained in many different ways known in the art, such asapplying a sine/frequency sweep to obtain response values for each of avariety of frequencies across a chosen frequency range (such as, forexample, the operational frequency range of the actuator/bone conductiondevice). Each exemplary actuator is in a different state. Frequencyresponse plot 505 represents the frequency response for the impedancemagnitude of an actuator that is securely attached or fullyosseointegrated to the recipient. It should be recognized that “fully”osseointegrated as used herein may include an actuator, or an implantedanchor such as implanted anchor 162 to which the actuator is connected,that is substantially, or almost, osseointegrated into the skull of arecipient such that the osseointegration is sufficient for the recipientto use the actuator as a component of a hearing prosthesis withoutcausing damage to the actuator or to the recipient. For example, theactuator is not unstable or loose from the head of the recipient that itis attached to. Since a stable actuator connection is ideal for a boneconduction device that is coupled to a recipient using a rigidpercutaneous abutment, this state of the actuator may be consideredbelow to be an “ideal” actuator state for that type of connection, aswill be described further. Frequency response plot 510 represents thefrequency response for the impedance magnitude of an actuator that isunstable, or loosely attached to the recipient. For example, theactuator may be damaged, the implant may be loose, or the implant mayhave not fully osseointegrated with the bone of the recipient with whichit is attached after surgery. In another embodiment, the actuator may beheld by a softband that is configured to be worn around the recipient'shead. In other embodiments, the actuator may be connected to the skullof the recipient using an adhesive, a testband, test rod, atranscutaneous device using transmission of data via magnets, or othertypes of bone conduction devices including actuators that are notimplanted in the skull of the recipient. When a softband or othernon-implanted system is used, the actuator may be pushed against therecipient's skull to transmit vibrations to the skull, but is notrigidly connected to the skull. Frequency response plot 515 representsthe frequency response for the impedance magnitude of an actuator thatis disconnected from the recipient. For example, the actuator may beheld in the recipient's hand or may be lying on a table while therecipient is sleeping.

As can be seen in FIG. 5A, frequency responses 505, 510 and 515 of themagnitude of the impedances of the actuator across the chosen frequencyrange vary. For example, between the frequencies of approximately 0.4kHz (400 Hz) and 4 kHz (4000 Hz), frequency response plots 505, 510 and515 show varying magnitudes. More specifically, at those frequencies,the actuator has different magnitudes of impedance across it. Thecomparison of plots 505, 510 and 515 shows that when the impedanceacross the actuator varies, the actuator may have different stabilitiesor may be connected to the recipient in different ways (again, referredto herein as actuator characteristics or states), as will be describedfurther.

Embodiments include various techniques that can use impedance dataprovided by an actuator, such as the data in the frequency responsesshown in FIG. 5A for the magnitude of the impedance of the actuator, tomake determinations about the state of the actuator. For example, first,the magnitude of the impedance of an actuator may be compared to athreshold, such as the magnitude of the impedance of a predetermined“ideal” (i.e. ideally stable) actuator. For example, if the actuator isintegrated into a bone conduction device, then the threshold “ideal” orexpected frequency response may be, for example, (1) the frequencyresponse of the same actuator taken at a time when the device was knownto be stable and fully osseointegrated into the skull of the recipient,(2) the frequency response of a different device that is stable andfully osseointegrated into the same recipient at a previous time, or (3)the frequency response of the actuator taken from a simulation. Thisprocess may be completed by, for example, an audiologist when examininga recipient after the recipient has undergone surgery to implant a boneconduction device.

For example, as noted, frequency response plot 505 could be used as athreshold, or in other words the frequency response of an actuator takenat a time when the device was known to be stable and fullyosseointegrated into the skull of the recipient. Then, when running atest on a recipient, an audiologist may compare corresponding data takenfrom the recipient's actuator to the threshold data. The audiologist mayreceive and analyze raw data, or may receive a result/conclusion afterthe raw data has already been analyzed by the DSP within the device.Such a result may include a conclusion that the actuator is unstable, oran even more specific conclusion such as, for example, that the actuatoris unstable and will require three more days until stability is reachedat the (then) current rate of osseointegration. If frequency responseplot 510 was taken as the frequency response representing an actuatorbeing used in a hearing prosthesis of a recipient, then the system or anaudiologist may compare frequency response plot 510 with thresholdfrequency response plot 505 to observe any differences in impedancemagnitude. More specifically, the audiologist may select one or morefrequencies for which to compare the impedance magnitude (in thisexample, by comparing plot 510 with the threshold impedance magnitude ofplot 505). For example, if the audiologist selected a frequency of 1kHz, then the comparison would show an impedance magnitude ofapproximately 35 Ohms as compared to a threshold impedance magnitude ofapproximately 25 Ohms, as shown by plots 505 and 510 in FIG. 5A. Thedifference of 10 Ohms between the measured value and threshold valuewould indicate to the audiologist that the recipient's actuator is, forexample, unstable. In other words, the increase in impedance magnitudewould indicate a move from more a stable to a less stable implant.

In an exemplary embodiment, the magnitude of the impedance of theactuator can be determined through the use of two different measurementsobtained at or during the same temporal period (e.g., simultaneously).By way of example only and not by way of limitation, a voltage and acurrent across an actuator can be determined. That said, alternativelyand/or in addition to this, voltage and/or current determinations can bemade at other locations, such as, for example, voltage output from anamplifier. Any device, system and/or method that can enable themagnitude and/or phase of the impedance of the actuator to be determinedcan be utilized in at least some embodiments.

Referring again to FIG. 5A, if plot 515 represents the frequencyresponse of the magnitude impedance of the recipient's actuator, then anaudiologist may compare frequency response plot 515 with thresholdfrequency response plot 505 to observe any differences in impedancemagnitude. If the audiologist selected the same frequency of 1 kHz forcomparison, then the comparison would show an impedance magnitude ofapproximately 44 Ohms as compared to a threshold impedance magnitude ofapproximately 25 Ohms. The difference of 19 Ohms between the measuredvalue and threshold value would indicate to the audiologist that therecipient's actuator is even more unstable. For example, such adifference may indicate to the audiologist that the actuator is notconnected to the recipient's skull at all, and instead is either in therecipient's hand or lying on a table while the recipient is sleeping.

As noted, the DSP or audiologist may read the magnitude impedance ofmore than one frequency. If the DSP or audiologist were to only readimpedance data for one sample frequency, the comparison of thisimpedance data to the threshold data at that frequency may yield a falsenegative. For example, if the audiologist chose 700 Hz, then bothrepresentative plot 510 and 505 would yield a magnitude of approximately38 Ohms. The audiologist may then assume that the implant is fullystable although, as shown by magnitude impedance data for most otherfrequencies between 400 Hz and 4 kHz, the actuator is in fact unstableor loose.

As noted, an actuator may be held by a passive transcutaneous, softbandor testband bone conduction device or may be connected to the head inother ways, such as via an adhesive. For such a device, the “ideal” orthreshold magnitude impedance may be represented a less stable frequencyresponse since such a system provides for the actuator to be, as noted,pushed up against the recipient's skull to transmit vibrations to theskull, but not rigidly connected to the skull. Therefore, the thresholdmagnitude impedance frequency response may be plot 510 instead of plot505.

Referring back to FIG. 5A, if the audiologist selected a frequency of800 Hz, the comparison would show an impedance magnitude ofapproximately 25 Ohms as compared to a threshold impedance magnitude ofapproximately 35 Ohms. While such a comparison would show a decrease inmagnitude impedance, this difference also represents a change inimpedance and may also indicate a shift in the stability of theactuator. A drastic decrease in magnitude impedance may indicate thatthe actuator has been re-connected to the skull of the recipient afterbeing previously decoupled after an accident or removal by the recipientfor sleeping or another purpose.

Some exemplary embodiments will be detailed herein that enable thedetermination of a change in the impedance of the actuator. It is notedthat any device, system and/or method that can enable a determinationthat a change of an impedance of the actuator has taken place can beutilized in at least some embodiments.

It is further noted that a change in the overall system can result in achange in the impedance of the actuator. As is explained in more detailelsewhere, the actuator itself may not change, but the system in whichit is used may change (e.g., mechanical aspects of a coupling thatplaces the actuator in vibrational communication with the recipient canchange over time, and this will result in a change in the impedance ofthe actuator because it is mechanically linked to the coupling).

Furthermore, the magnitude of the impedance may instead be observed fordifferences in magnitude between multiple frequencies. Morespecifically, the audiologist may read the magnitude of the impedance attwo different frequencies, calculate the difference in magnitude betweenthe two frequencies, and then compare that difference to a threshold.For example, the audiologist could calculate the difference in magnitudebetween 0.7 kHz (700 Hz) and 0.9 Hz (900 Hz). If frequency response plot510 represents the frequency response of the recipient's actuator, thenthe difference in impedance magnitude between 700 and 900 Hz would becalculated by the audiologist as an increase of approximately 4 Ohms(from 39 Ohms to 43 Ohms). If plot 505 represents the frequency responsethreshold, the threshold difference between the two frequencies would beapproximately 10 Ohms (from 37 Ohms to 27 Ohms). This change in thedifference between magnitudes of impedance at different frequencieswould indicate to the audiologist that the recipient's implant haschanged in stability, such as, for example, indicating a shift from morea stable to a less stable actuator.

A second technique that uses impedance data provided by an actuator tomake a determination of the state of the actuator is to observe themagnitude of the impedance of an actuator for changes over time. Forexample, an audiologist may observe magnitude impedance data from therecipient's actuator at a certain selected frequency, and then comparethat data to similar data from the actuator at the same frequency at alater time. If a change in the magnitude of impedance across theactuator is different at the later time, then this change in impedancemay indicate a change in state or characteristic of the actuator, suchas that an implant has become more unstable or, for a more drasticincrease, that the device has been detached from the recipientaltogether. For example, if the frequency response of the magnitudeimpedance of the actuator at a certain frequency at a first time wasrepresented by plot 505, and the audiologist chose to sample themagnitude impedance at 0.6 kHz (600 Hz), then the audiologist would reada magnitude of about 39 Ohms. If the actuator became loose, was detachedfrom the head or was otherwise adjusted by accident or on purpose, thenthat magnitude may change accordingly. Therefore, if the audiologistreads the magnitude impedance at the same 0.6 kHz (600 Hz) frequency ata later time, the magnitude may be higher or lower than 39 Ohms,indicating such a change in status of the actuator. For example, if thefrequency response of the magnitude impedance of the actuator at thelater time was represented by plot 510, then the audiologist would reada magnitude of about 34 Ohms. The 5 Ohm drop between two different times(which may be less than a second, seconds, minutes, hours, days ormonths apart) represents, as noted, a change in status such as a changein stability of the device.

Third, magnitude of the impedance of an actuator may be observed usingresonance peaks of the frequency response of the magnitude impedance ofthe actuator. A resonance peak of a frequency response refers to thefrequencies or frequencies at which a peak in the amplitude of thefrequency response of the system occurs. Therefore, observing andcomparing resonance peaks of the frequency response of the magnitudeimpedance to either the expected resonance peak of the frequencyresponse of the magnitude impedance for an “ideal” actuator connectionwith the recipient, such as the threshold frequency response described,or to the resonance peak of the frequency response of the magnitudeimpedance at a previous point in time, may indicate a change in state ofthe actuator.

FIG. 5B illustrates three frequency responses for the phase of theimpedance (hereinafter “impedance phase”) of, for example, the actuatorin FIG. 1A. Frequency response plot 520 represents the frequencyresponse for the impedance phase of an actuator that is securelyattached to the recipient (and, for example, not unstable or loose).Frequency response plot 525 represents the frequency response for theimpedance phase of an actuator that is unstable, or loosely attached tothe recipient. Frequency response plot 530 represents the frequencyresponse for the impedance phase of an actuator that is disconnectedfrom the recipient. Similar conclusions may be drawn from the frequencyresponse for the impedance phase of an actuator as from the frequencyresponse for the impedance magnitude of that actuator. For example, thephase of the impedance of an actuator may be compared to a threshold,such as the phase of the impedance of a predetermined expected, ideal orbaseline actuator. The phase of the impedance of an actuator may also beobserved for changes over time. Furthermore, the phase of the impedanceof an actuator may be observed using resonance peaks of the frequencyresponse of the phase impedance of the actuator.

As can be seen in FIG. 5B, the actuator has varying frequency responsesof the phase of its impedance in different states. For example, betweenthe frequencies of approximately 0.4 kHz (400 Hz) and 3 kHz (3000 Hz),frequency response plots 520, 525 and 530 show varying phases. Morespecifically, at those frequencies, the actuator has different phases ofimpedance across it. This comparison represents that the actuator mayhave different stabilities or may be connected to the recipient indifferent ways, as described above with respect to magnitude. One ofordinary skill in the art would appreciate that similar techniques asthose described above with respect to observing changes in the magnitudeimpedance of an actuator may be applied similarly to changes in thephase impedance of an actuator.

Embodiments of the present technology have been discussed with referenceto measuring and storing data related to frequency responses of theimpedance of an actuator for the purpose of an audiologist using thatdata to make assumptions about the status or characteristics of thehearing prosthesis. However, the data may also be used internally by thedevice itself to, as noted, improve the accuracy of mechanicalstimulation delivered to the recipient. More specifically, the frequencyresponse of the impedance across an actuator in a bone conduction deviceis used by the stimulator unit, such as stimulator unit 149 in FIG. 1A,in generating the drive signals provided to the actuator in processingreceived sound and causing a hearing percept by the recipient. Forexample, in certain embodiments, as noted, the actuator may have sharpresonance peaks, which indicate a spike in impedance across theactuator. For another example, changes in impedance across an actuatormay otherwise indicate that the actuator is unstable, that the actuatoris being used in a softband, or other functional states. Measuring thefrequency response (and, for example, determining resonance peaks of thefrequency response) by measuring changes in impedance of the actuator,allows the stimulator unit to compensate for (e.g., using software) theinstability of the system, resonance peaks or other problems with theactuator. For example, the control circuit (e.g., DSP) may compensatefor a lower transmission of sound to the cochlea by the softband,re-calibrate the frequency response output levels, among other remedies.Depending on the actuator type this compensation may be useful fordifferent reasons. For example, sharp changes in resonance or actuatorimpedance can cause feedback to occur at those frequencies. Further,such changes can result in the power consumption becoming too high,distortion of the stimulation since the actuator may start to behavenon-linearly, or even over-stimulation that may result in hearing damageif not properly controlled.

As would be appreciated by one of ordinary skill in the art, the datashown in FIGS. 5A and 5B, including magnitudes, phases and frequencies,are provided for illustration purposes only. The actual data may varydepending on the individual and application of the present technology.As such, these illustrative examples should not be construed as limitingthe present invention.

Exemplary devices for measuring changes in impedance of an actuator insuch a vibrating hearing prosthesis are described below with respect toFIGS. 2A and 2B. For ease of explanation, only those components of thebone conduction device that will be discussed below are illustrated inFIGS. 2A and 2B, and in actual implementation additional components maybe included, such as actuator drive components, etc.

FIG. 2A is a simplified block diagram of a housing of an exemplary boneconduction device 200A, such as the bone conduction device of FIG. 1A.As illustrated, housing 124 includes a sound input device 126, a controlcircuit 208, a signal generator 222, an amplifier 217, an actuator 140and a shunt resistor 205. Control circuit 208 is a circuit configuredfor exercising control over the bone conduction device. For example,control circuit 208 is configured for receiving, from the sound inputdevice 126, sound waves from the recipient's environment. Furthermore,control circuit 208 is configured to process the audio signals togenerate control signals for controlling signal generator 222 ingenerating drive signals causing actuation of actuator 140. Controlcircuit 208 may include a digital signal processor (DSP) and/or othercomponents to control the other components within housing 124.Alternatively, the control circuit 208 may comprise a controller such asa microprocessor or a software based controller. The control circuit 208may comprise either digital circuitry or analog circuitry. It should beunderstood the term control circuit can include any control device orsystem.

Signal generator 222, as noted above, generates the drive signals forcausing actuation of actuator 140. After signal generator 222 sends adrive signal towards actuator 140, it is amplified by amplifier 217.Amplifier 217 is controlled by control circuit 208 and, in conjunctionwith signal generator 222, determines the amplitude and othercharacteristics of the drive signal sent to actuator 140. Actuator 140is any type of suitable transducer configured to receive electricaldrive signals and generate mechanical motion (e.g., vibrations) inresponse to the received electrical signals.

Shunt resistor 205 is electrically connected in series to actuator 140,and may be used for the purpose of measuring the impedance acrossactuator 140. A shunt resistor, also known as an ammeter shunt, is a lowresistance precision resistor used to measure AC or DC electriccurrents. However, a shunt resistor may include various other types ofresistive elements, instead of or in addition to a typical, stand-aloneshunt resistor, used to represent such a low resistance path, such aselectrostatic discharge (ESD) components. Such ESD components may beotherwise present in housing 124 to relieve the system of static thatcould damage wires or other components within any integrated circuitryin housing 124. Therefore, no extra components may be necessary toprovide a shunt resistor for measuring impedance. Shunt resistorsgenerally allow electric currents to pass through it by creating a lowresistance path that attracts current towards that path and has ameasurable change in electrical impedance either in the time domain orin the frequency domain. Collectively, components such as shuntresistors or other resistive elements that act similar to shuntresistors for the purpose of providing a low resistance path, asdescribed above, may be called “shunt components.” Examples of suchshunt components may include typical, stand-alone shunt resistors,electrostatic discharge (ESD) components, capacitors, diodes, amongothers.

FIG. 2B is a simplified block diagram of a stimulator unit andstimulation arrangement of an exemplary middle ear implant. Thecomponents of system 200B are similar to bone conduction device 200A,except that the components are divided in between stimulator unit 149and stimulation arrangement 150B. For example, as shown in FIG. 2B,control circuit 208, signal generator 222 and amplifier 217 may beincluded within stimulator unit 149, while actuator 140 and shuntresistor 205 may be included within stimulation arrangement 150B.Alternatively, shunt resistor 205 may be included within control circuit208 or otherwise within stimulator unit 149. It would also beappreciated by a person of ordinary skill in the art that othercombinations of components, including extra components not shown in FIG.2A or 2B, are also contemplated within the scope of the currenttechnology.

To determine a change in impedance across actuator 140, shunt resistor205 may be used. For example, since shunt resistor 205 has a knownresistance at manufacture, the voltage across shunt resistor 205 isproportional to the current flowing through shunt resistor 205.Furthermore, since shunt resistor 205 is connected to actuator 205 inseries, the current flowing through shunt resistor 205 is substantiallythe same as the current flowing through actuator 140. Therefore,measuring the voltage across shunt resistor 205 can be used to evaluatethe impedance across actuator 140 (including detecting a change ofimpedance or the impedance) and determining a change in voltage acrossshunt resistor 205 indicates a change in mechanical impedance acrossactuator 140. Therefore, determining a change in voltage across shuntresistor 205 corresponds to and/or is representative of a change inelectrical impedance across actuator 140 and, in turn, a change inmechanical impedance across actuator 140 for a given stimulus.Therefore, a change in the voltage across shunt resistor 205 isindicative of a change of impedance across actuator 140.

FIG. 3A is a flow chart 300A of an exemplary method for determining achange in impedance across actuator 140 using shunt resistor 205. First,as shown in block 302, a defined stimuli of a predetermined voltage issent to actuator 140. More specifically, control circuit 208 initiatesthe process by directing signal generator 222 to send a signal (stimuli)to actuator 140. As this defined stimuli is predetermined, it has aknown voltage and is applied to actuator 140.

As shown in step 304, the voltage across shunt resistor 205 is measured.As shown, for example, in FIG. 2A, shunt resistor 205 is connected onone side to actuator 140 and control circuit 208, and on the other sideto ground. Therefore, control circuit 208 can measure the voltage acrossshunt resistor 205 since it is connected to shunt resistor 205 oppositeto ground. As noted, control circuit 208 may include a digital signalprocessor (DSP). Therefore, shunt resistor 205 may be connected to, forexample, a general purpose input output (GPIO) of control circuit/DSP205, allowing the DSP to measure the voltage across shunt resistor 205.Alternatively, shunt resistor 205 may be connected to a microphone inputon the DSP, which will also allow the DSP to measure the voltage acrossshunt resistor 205. For example, the DSP may include four or moremicrophone inputs, only one or two of which are connected to sound inputdevice 126 for use to receive sound. Therefore, such a microphone inputmay be used to allow the DSP to measure the voltage across shuntresistor 205.

The use of control circuit 205 to measure the voltage across shuntresistor 205 is beneficial because the system does not further require aseparate component or set of components to measure the voltage acrossshunt resistor 205. For example, it is not necessary for the system toinclude one or more voltage measurement circuits, voltmeters,potentiometers, oscilloscopes, or other devices to measure voltage.Since one side of actuator 140 is connected to ground, control circuit208 may read the voltage across shunt resistor 205 while only beingconnected to one side of shunt resistor 205. Therefore, it is notnecessary to provide, for example, a voltage measurement circuit tomeasure the voltage on both sides of shunt resistor 205. This devicesetup provides the benefit of requiring less components, which savesspace and power consumption by the hearing prosthesis.

Referring back to FIG. 3A, after the voltage is measured across theshunt resistor, as shown in step 306, a second defined stimuli is sentto actuator 140. The second stimuli sent to actuator 140 in step 306 maybe at a different frequency than the first stimuli sent to actuator 140in step 302, or the second stimuli may be at the same frequency than thefirst stimuli, but may be sent at a different time than the firststimuli. These two possibilities are described further with respect toFIGS. 3B and 3C. Then, the voltage across shunt resistor 205 (i.e. theshunt component) is measured a second time in step 308.

Next, as shown in step 310 the voltage across shunt resistor 205 iscalculated based on the measured voltage from step 304 and the measuredvoltage from step 308. The calculated voltage difference is thenanalyzed to determine a change in impedance across actuator 205, whichcan be analyzed to monitor problems or other characteristics/statuses ofthe actuator. For example, as noted, this impedance difference may becompared to the same calculated difference of a threshold, ideallystable actuator, or to the same calculated difference of the sameactuator at a different point in time. If compared to a threshold, thenthe voltage difference would be compared to a value stored in memory,either in the control circuitry or elsewhere in system 200. If comparedto the same calculated difference of the same actuator at a differentpoint in time, the same process of steps 302-310 would be performed atthat different point in time, and the voltage differences at those twodifferent times would be compared.

FIG. 3B is a flow chart 300B of another exemplary method for determininga change in impedance across actuator 140 using shunt resistor 205. Asnoted, observing the magnitude of the impedance of an actuator forchanges over time may be used to make a determination of the state ofthe actuator. For example, an audiologist may observe magnitudeimpedance data from the recipient's actuator at a certain selectedfrequency, and then compare that data to similar data from the actuatorat the same frequency at a later time. If a change in the magnitude ofimpedance across the actuator is different at the later time, then thischange in impedance may indicate a change in state or characteristic ofthe actuator. FIG. 3B illustrates this exemplary method.

First, as shown in block 320, a first defined stimuli of a predeterminedvoltage is sent to actuator 140. More specifically, control circuit 208initiates the process by directing signal generator 222 to send a signal(stimuli) to actuator 140. As this defined stimuli is predetermined, ithas a known voltage and is applied to actuator 140.

As shown in step 322, the voltage across shunt resistor 205 is measured,similar to step 304 in FIG. 3A. Then, as shown in block 324, the systemdelays for a predetermined amount of time, labeled t_(Δ). At block 326,a second defined stimuli of a predetermined voltage is sent to actuator140 and, again, the voltage across shunt resistor 205 is measured atblock 328. This process yields two measurements of voltage across theshunt resistor, each at a different point in time. As shown in block310, the difference between these two measured voltages is thencalculated. Such a voltage difference may be compared to a thresholdvoltage difference, or the measurement taken at the later time (t+t_(Δ))may be compared to the earlier measured voltage. In either instance, asnoted, any change in impedance may indicate a state or change in stateof the actuator.

FIG. 3C is a flow chart 300C of another exemplary method for determininga change in impedance across actuator 140 using shunt resistor 205. Asnoted, observing the magnitude of the impedance of an actuator forchanges between different frequencies may be used to make adetermination of the state of the actuator. More specifically, theaudiologist may read the magnitude of the impedance at two differentfrequencies, calculate the difference in magnitude between the twofrequencies, and then, for example, compare that difference to athreshold. FIG. 3C illustrates this exemplary method.

First, as shown in block 340, a first defined stimuli of a predeterminedvoltage is sent to actuator 140. As shown in block 341, a second definedstimuli of a predetermined voltage is sent to actuator 140. The firstand second stimuli sent to actuator 140 are sent at different,predetermined frequencies. After the first stimuli is sent to theactuator, as shown in block 342, the voltage across shunt resistor 205is measured, similar to step 306 in FIG. 3A and step 322 in FIG. 2B.After the second stimuli is sent to the actuator, as shown in block 343,the voltage across shunt resistor 205 is measured.

Next, as shown in block 344, the difference between these two measuredvoltages is then calculated. Such a voltage difference may be comparedto a threshold voltage difference, as shown in block 345, or may becompared to a similar difference previously taken between the same twofrequencies. In either instance, as noted, any change in impedance mayindicate a state or change in state of the actuator. In an exemplaryembodiment, this threshold voltage can be stored in the device (e.g.,can be part of an algorithm used to determine the change in theimpedance).

Although FIGS. 3A-3C were not each described in the context ofimplementing each process of calculating a change in impedance acrossactuator 140 or of determining a state or characteristic of the actuatorbased on that change in impedance, it should be recognized that suchmethods should be considered as part of the scope of the presenttechnology.

Instead of measuring a change in voltage across shunt resistor 205which, as described, is proportional to the current flowing through thesystem and is representative of a change in impedance across actuator140, one may instead use the measured values of voltage across shuntresistor 205 to actually calculate that current and subsequently achange in electrical impedance of actuator 140. As noted, a change inelectrical impedance presented by the actuator indicates a correspondingchange in mechanical impedance of the actuator. FIG. 4 shows a partialcircuit diagram, a voltage divider, representative of the actuator andshunt resistor relationship described above with respect to FIGS. 2A, 2Band 3. Circuit diagram 400 includes Z_(unknown) 440, which representsthe complex electrical impedance of actuator 140, and R_(shunt) 405,which represents the resistance of shunt resistor 205. Furthermore,V_(known), shown next to Z_(unknown) 440 in FIG. 4, is the known voltageapplied to actuator 140. Z_(unknown) 440 is known because it is equal tothe voltage stimulus applied to actuator 140 by signal generator 222, asdescribed. V_(Rshunt) represents a voltage, or a change in voltage,across R_(shunt). Since the change in voltage across R_(shunt) isproportional to the current through R_(shunt), and therefore the currentthrough actuator 140, the following equation may be used to determineZ_(unknown):

Z_(unknown) = (R_(shunt) * V_(known))/V_(Rshunt)

Since R_(shunt)*V_(known) are known and V_(Rshunt) is calculated, asdescribed, Z_(unknown) may be calculated.

As noted, the bone conduction device may also include a power source togive power to the different components of the external or implantedcomponent, such as amplifier 217 shown in FIGS. 2A and 2B. When fullypowered and in fully working condition, the power source applies a knownvoltage to the device components (at least partially resulting in aknown V_(known) as described above). However, if the power source hasdeteriorated over time, then the “known” voltage being applied may notaccurately reflect the actual voltage being applied. Such deteriorationmay be detected using a built-in detector or a change in impedance inthe system as described herein. This deterioration may be compensatedfor after detection in the calculation of the impedance across theactuator as described above.

As noted, once a change in impedance of an actuator in a vibratinghearing prosthesis has been detected and analyzed, that change inimpedance may be used for various purposes. More specifically, datacollected regarding the change in impedance of the actuator may be usedto benefit the recipient and improve the performance of the hearingprosthesis. First, as noted, a change in impedance across actuator 140may indicate a change in the stability of the implant. A change instability of the implant may indicate one or more of several states orconditions of the implant, such as that the connection between theactuator and the skull of the recipient, has become looser than it waspreviously. An implant may become looser over time for various reasons.For example, an implant may become looser over time because therecipient fell or otherwise hit their skull and/or hearing prosthesisagainst a hard surface. This may especially be a problem for youngchildren who tend to be more reckless than adults and do not protectthemselves from damage and resultant trauma. If a child, or anotherrecipient, were to experience trauma to the head, an audiologist orcaretaker for the recipient (hereinafter, collectively, “the recipient”)may initiate a test to measure the change impedance across the actuator.This data, including the change in impedance across the actuator, may besent to the audiologist for analysis or may be viewed and analyzed on acomputer by a caretaker for the recipient. If it is determined that theimplant has become looser over time, then the recipient may choose tohave the device re-attached to the skull or other remedies.

An implant may also become looser over time because the implanted sitewithin the recipient has not healed correctly, causing osseointegrationbetween the bone conduction device and the skull of the recipient tostall and even regress. The use of actuator impedance data to detect thestatus of osseointegration is discussed further below.

An implant may also become looser over time because the implantcomponents may have corroded or otherwise become less structurallysecure over time. For example, the coupling (such as coupling 161 inFIG. 1A), implanted anchor (such as implanted anchor 162 in FIG. 1A), orother abutment physically coupling the external portion of the boneconduction device to the recipient, or the actuator itself or otherportions of the external component, may have worn over time and may needto be replaced. If it is determined that the implant has become looserover time, then the recipient may choose to have the whole device orparts of the device replaced.

An implant may also change stability by becoming more stable over time.For example, an implant may become more stable over time in the weeksand months after surgery, during which a surgeon implanted the boneconduction device into the recipient's skull. As such, a change instability may indicate a change in the status of osseointegrationbetween the implant and, in the case of a bone conduction device, theskull of the recipient. Osseointegration begins immediately aftersurgery and occurs over time until the implant is fully stable/implantedinto the recipient. Therefore, if the surgery to implant the boneconduction device was successful, actuator 140 should be in its leaststable state immediately after surgery and should become more stableover time. Therefore, a change in impedance across actuator 140 overtime, such as a gradual and steady decrease in impedance, may indicatethat the bone conduction device is successful osseointegrating with theskull of the recipient and the site of surgery is healing correctly. Onthe other hand, a constant or slowly decreasing impedance acrossactuator 140 over time may indicate that the bone conduction device isnot osseointegrating with the skull of the recipient and/or the site ofsurgery is not healing correctly. If this state is determined, then therecipient may choose to adjust the implant or re-introduce the implantto the skull of the recipient in a different manner.

If the impedance across actuator 140 gradually and steadily decreasesover time after implantation and is compared with a threshold, such asthe predetermined impedance of an ideal device that has fullyosseointegrated into the skull of the recipient, then this data may helpa recipient or audiologist determine that the bone conduction device isready to be operated for the first time. For example, the change inimpedance across actuator 140 within a fully osseointegrated boneconduction device should be equal to or close to zero since the actuatorin a fully osseointegrated device should be stable. On the other hand,if the impedance across the actuator in the bone conduction device isstill changing over time, then use of the actuator, which would requirevibration of the actuator, may cause the stability of the implant todecrease or prevent the implant from continuing to stabilize aftersurgery. Therefore, a recipient or audiologist may initiate a test todetermine the impedance across the actuator in a recently implanteddevice to determine when the device is ready for use by the recipient.

Second, a change in impedance across actuator 140 may indicate what typeof device the actuator is connected to. As noted, the actuator may beincluded in a bone conduction device that is coupled to the skull of arecipient using an abutment (including, for example, a coupling such ascoupling 161 in FIG. 1A, an implanted anchor such as implanted anchor162 in FIG. 1A, among others). When such an abutment is used, the boneconduction device, including the actuator, is rigidly coupled to theskull of the recipient. On the other hand, the actuator may be includedin a softband bone conduction device that is configured to be wornaround the recipient's head. When a softband is used, the actuator maybe pushed against the recipient's skull to transmit vibrations to theskull, but is not rigidly connected to the skull. Since bone conductiondevices using, for example, an abutment and a softband are coupled tothe recipient's skull with different rigidities, the stability of theactuator in those devices will also be different. More specifically, anactuator in a softband bone conduction device will be generally be lessstable than an actuator in a bone conduction device that couples theactuator to the skull of a recipient using an abutment. Therefore, anaudiologist or recipient may initiate a test to determine the impedanceacross the actuator and compare that impedance to a threshold, such asthe impedance across the actuator of a bone conduction device that has aknown coupling mechanism.

Similarly, if the actuator is implemented into an external componentthat is indirectly connected to the recipient's skull by connecting theexternal component to the skin of the recipient adjacent to the skullusing, for example, an adhesive, a change in impedance across theactuator may help detect if the adhesive is deteriorating over time. Forexample, an increase in mechanical impedance of the actuator over timemay indicate an increase in instability, as noted, and the increase instability may indicate that the adhesive is not securely holding theexternal component to the recipient's skin any longer. If the adhesivehas become looser over time, the recipient may choose to replace theadhesive, or re-attach the external component to their skin using newadhesive.

Third, a change in impedance across actuator 140 may indicate whetherthe bone conduction device is being worn by the recipient or whether thebone conduction device has been disconnected from the recipient and isinstead detached from the recipient (such as, for example, being held inthe recipient's hand or lying on a table). Generally, bone conductiondevices and other hearing prostheses include a user interface with userinterface elements, such as buttons and switches, that allow therecipient and/or audiologist to control certain features of the boneconduction device. One example of a feature that the recipient and/oraudiologist may control is whether the bone conduction device is turned“on” for when the recipient is wearing and using the hearing prosthesis,or “off” for when the bone conduction device is not being used. However,it is possible that the recipient may detach the bone conduction device,whether coupled to the recipient's head using an abutment or a softband,and forget to turn the device off. For example, a recipient may detachthe bone conduction device before going to sleep at night and leave thedevice on a table. Forgetting to turn the device off when not being usedfor long periods of time will drain the battery within the boneconduction device and render the bone conduction device unusable thenext time that the recipient chooses to use the device. An actuatorwithin a bone conduction device vibrating freely without being connectedto a recipient may also result in damage to the device.

Alternatively, after implementing embodiments of the present technologyinto the bone conduction device, the device may instead run periodictests on the device, including collecting data on changes in impedanceacross actuator 140. For example, control circuit 208, which may includea DSP, may initiate a test of the bone conduction device by directingsignal generator 222 to send a defined signal (stimuli) of apredetermined voltage to actuator 140, measuring the voltage acrossshunt resistor 205, and calculating changes in impedance across theshunt resistor and actuator over time, as described. These voltagemeasurements and changes in impedance may then be stored in memorywithin control circuit 208 or elsewhere within the bone conductiondevice. If a drastic change in impedance across actuator 140 isdetected, as described with respect to FIG. 5A, then control circuit mayconclude that the bone conduction device has been disconnected from therecipient and can opt to automatically turn off the bone conductiondevice. Such a conclusion can be drawn regarding a bone conductiondevice that is completely disconnected from the recipient becauseactuator 140 would vibrate free in air when vibrating, resulting in ahigh peak impedance, as described.

Similarly, if little or no impedance is detected across actuator 140, itmay be determined that the actuator has temporarily failed or otherwisestopped working. Such a state of the actuator could be a serious problemfor the recipient because the recipient may unexpectedly be unable tohear using the bone conduction device.

After a state of the bone conduction device has been detected, such as,for example, instability of the device, the device may notify therecipient that a problem exists in the bone conduction device. Forexample, the device may automatically send an alert to a remote devicesuch as a smartphone. Such an alert would allow the recipient oraudiologist to take action to fix any problem detected in the boneconduction device, or otherwise take action based on the state of thedevice. The device may also output an audible alert using a speaker orother transducer (not shown) to notify the recipient that a problemexists in the device.

Exemplary methods can be used with a bone conduction device such as thatdisclosed in U.S. patent application Ser. No. 13/723,802, filed on Dec.21, 2012, naming Dr. Marcus Andersson as an inventor. With regard tothat application, an exemplary bone conduction implant as detailedtherein includes a bone fixture configured to screw into the skull bone,a skin-penetrating abutment and an abutment screw that is in the form ofan elongate coupling shaft. The bone conduction device of thatapplication is configured such that the operationally removablecomponent is removably attached to the implant. This is accomplished viaa coupler, a portion of which is included in the bone conductionimplant, and a portion of which is included in the operationallyremovable component. In an exemplary embodiment, the operationallyremovable component snap-couples to the abutment. The abutment includesa recess formed by sidewalls thereof that has an overhang thatinterfaces with corresponding teeth of coupling apparatus. Teethelastically deform inward upon the application of sufficient removaland/or installation force to the coupling apparatus. In the embodimentof the just-referenced application, the connection between the couplingapparatus and the abutment is such that vibrations generated by theoperationally removable component (e.g., such as those generated by anelectromagnetic actuator and/or a piezoelectric actuator, etc.) inresponse to a captured sound are effectively communicated to theabutment so as to effectively evoke a hearing percept, if not evoke afunctionally utilitarian hearing percept. Such communication can beachieved via a coupling (sometimes referred to as a connection orcoupler) that establishes at least a modicum of rigidity between the twocomponents.

In this vein, the dimensions and/or geometries of the interfacingportions are, in at least some embodiments, are specific and highlytolerance to provide a utilitarian bone conduction hearing percept.

In an exemplary embodiment, there is a method that includes utilizingthe techniques detailed herein to determine one or more characteristicsof the coupling between the operationally removable component and theabutment. For example, determining that a change in the impedance of theactuator of the bone conduction device can be used to determine that themechanical characteristics of the coupling have changed (e.g., in thecase of a snap-coupling, the teeth of the coupling have worn down and/orthe resiliency of the teeth has deleteriously changed and/or theabutment has worn down, etc.

Accordingly, there is a method, comprising determining a change in anactuator impedance based on a change in an electrical property of asystem of which the actuator is apart, and determining one or moresystem characteristics based on the change in the actuator impedance,wherein the system characteristic(s) are attrition (e.g., wear, damage,fatigue) of the coupling between the implant and the operationallyremovable component (e.g., one or both of the components that form thecoupling). In an exemplary embodiment, there is a method, comprisingapplying a first stimuli to an actuator that is part of a system,determining a change in voltage across a shunt component in series withthe actuator, and determining one or more system characteristics basedon the change in voltage, wherein the system characteristic(s) areattrition (e.g., wear, damage, fatigue) of the coupling between theimplant and the operationally removable component (e.g., one or both ofthe components that form the coupling). In an exemplary embodiment, thesystem characteristic(s) are the dimensions and/or geometries and/orchanges in the dimensions and/or changes in the geometries of theinterfacing portions of the coupling. In an exemplary embodiment, thesystem characteristic(s) are a thickness and/or a change in the skinthickness of a passive transcutaneous system (i.e., the thickness of theskin between the external component and the internal component thereof).In an exemplary embodiment, the system characteristic(s) are a holdingforce and/or a change in the holding force between the externalcomponent and the internal component of a passive transcutaneous system.In an exemplary embodiment, there is a method corresponding to any ofthose detailed herein that further includes utilizing existing signalsfor start-up, program change or volume change of a given hearingprosthesis that provides known output signals. These signals are used toestimate the actuator impedance and compare the impedance with referenceimpedances (including prior measured impedances). In an exemplaryembodiment, the signals are utilized such that the recipient is notexposed to additional signals beyond those that are currently present inhearing prostheses.

The technology described and claimed herein is not to be limited inscope by the specific preferred embodiments herein disclosed, sincethese embodiments are intended as illustrations, and not limitations, ofseveral aspects of the technology. Any equivalent embodiments areintended to be within the scope of this technology. Indeed, variousmodifications of the technology in addition to those shown and describedherein will become apparent to those skilled in the art from theforegoing description. Such modifications are also intended to fallwithin the scope of the appended claims.

What is claimed is:
 1. A method, comprising: applying a first stimuli toan actuator that is part of a prosthesis system; determining a change inan electrical property of an electrical arrangement which powers theactuator; and determining one or more system characteristics based onthe change.
 2. The method of claim 1, further comprising: determining achange in an impedance feature of an RF coil in signal communicationwith the actuator based on the determined change in the electricalproperty, wherein the determined change in the impedance feature is thedetermined change in the electrical property.
 3. The method of claim 1,further comprising: measuring a first voltage responsive to the firststimuli; applying a second stimuli to the actuator at a same frequencyas that of the applied first stimuli but at a different temporallocation than that of the first stimuli; measuring a second voltage,responsive to the second stimuli; and determining the change in voltagebased on the measured first and second voltage.
 4. A hearing prosthesis,the prosthesis comprising: an actuator; a signal generator configured toprovide a signal to the actuator to cause actuation of the actuator; anda control circuit configured to direct the signal generator to apply afirst stimuli to the actuator; wherein the control circuit is configuredto: determine a change in an electrical property of a system of whichthe actuator is apart; and determine an impedance-related phenomenon ofthe actuator based on the determined change in the electrical property.5. The auditory prosthesis of claim 4, wherein the control circuit isconfigured to direct the signal generator to generate and provide asecond stimulus, based on the determined impedance-related phenomenon,to the actuator.
 6. The auditory prosthesis of claim 5, wherein theimpedance-related phenomenon is at least one of a change in impedance oran impedance of an electrical system of which the actuator is apart. 7.A method for determining a state of a hearing prosthesis systemconfigured to deliver mechanical stimulation to a recipient via anactuator, wherein the system includes an external RF coil and animplanted RF coil, wherein the external coil is configured totranscutaneous communicate with the implanted coil to actuate theactuator, the method comprising: measuring a coil electrical property ofat least one of the external RF coil or the implanted RF coil; comparingthe measured coil electrical property to reference value(s); anddetermining one or more characteristics of the hearing prosthesis systembased on the comparison.
 8. The method of claim 7 further comprisingidentifying a change in impedance of the system based on the coilelectrical property and the reference value(s), wherein determining theone or more characteristics of the hearing prosthesis system is based onthe change in the impedance.
 9. The method of claim 7, wherein thecharacteristic of the hearing prosthesis system is that the actuator hasdecreased in stability with respect to a bone of the recipient.
 10. Themethod of claim 7, wherein the characteristic of the hearing prosthesisis that a component of the actuator of the hearing prosthesis has beenphysically disconnected from the recipient.
 11. The method of claim 7,wherein the characteristic of the hearing prosthesis is that a componentof the actuator of the hearing prosthesis has fully osseointegrated witha bone of the recipient.
 12. The method of claim 7, further comprisingdetermining a resonance peak of a frequency response of the impedance ofthe actuator.
 13. The method of claim 12, wherein determining one ormore characteristics of the hearing prosthesis comprises comparing theresonance peak with a threshold resonance peak.
 14. The method of claim7, wherein: the measured coil electrical property is a coil impedancemagnitude.
 15. The method of claim 7, wherein: the measured coilelectrical property is a coil impedance phase.
 16. The auditoryprosthesis of claim 4, further comprising: an external RF coil antenna;and an implantable RF coil antenna, wherein the prosthesis is configuredsuch that the external coil transcutaneously communicates with theimplanted coil, and the change in the electrical property of the systemis a change in an electrical property of at least one of the externalcoil and the implantable coil.
 17. The method of claim 2, whereindetermining the change in impedance of the actuator comprisesidentifying a change in the phase of the impedance of the actuator. 18.The auditory prosthesis of claim 4, wherein the system includes a shuntcomponent connected with the actuator in series, and wherein the changein the electrical property is a change in voltage across the shuntrelated to the first stimuli.
 19. The auditory prosthesis of claim 4,wherein the system includes a shunt component connected with theactuator in series, and wherein the change in the electrical property isa voltage difference across the shunt related to the first stimuli. 20.The auditory prosthesis of claim 4, wherein the hearing prosthesis is abone conduction device.
 21. The method of claim 7, wherein thecharacteristic of the hearing prosthesis is that the hearing prosthesisis a bone conduction device wherein the actuator is connected to theside of the head of a recipient via a device as one of the group of:softband bone conduction device, testband bone conduction device, testrod bone conduction device, active transcutaneous bone conduction deviceand passive transcutaneous bone conduction device.